1. Field of the Invention
This invention relates to a boot type seal especially adapted for ball and socket type joints. More particularly, it relates to a boot type seal for ball and socket type joints having a grease relief passage or passages on an outer surface thereof.
2. Related Art
Nearly all original chassis equipment, such as ball joints and tie rod ends, are sealed units. These “lube-for-life” parts are low maintenance since they are sealed, but generally do not have the longevity of a “greaseable” part. A greaseable part is one in which additional grease may be added periodically to replace grease which has escaped or broken down during use, thereby flushing old grease, debris associated with wear of the joint parts or other contaminants (e.g., moisture, dirt or the like) from the joint and replacing it with new grease to reduce friction and increase the service life of the component. Accordingly, greaseable parts are preferred for many applications, particularly in the automotive aftermarket and service parts markets. One challenge faced when designing a dust boot for a greaseable part is that the dust boot must serve as a barrier to prevent contamination from entering the articulating component. At the same time, the dust boot must allow grease, joint debris and other contaminants to escape when the part is flushed with new grease, such as by a repair technician, or when articulation of the joint or compression of the dust boot, or both, create conditions where there is an excess of grease within the dust boot or a portion thereof.
The dust boot is normally compressed against a control arm or other mating component of the suspension in conjunction with its installation. In some applications and joint designs where there is a large amount of stud swing, or where the boot is compressed against the control arm or other mating component over a relatively large portion of its surface area, a condition may arise where the dust boot surface may form an additional seal around the grease relief flap thereby preventing the release of grease from the grease relief passage. This becomes a concern when the stud is articulated in the same direction as the primary grease exit passage. In other words, the compression of the boot, particularly in the region of the grease evacuation flap, can result in trapped grease in the boot. If the dust boot is not able to release the grease, it may accumulate an excess of pressure causing the boot to burst or rupture during lubrication or operation of the joint, or for the grease to be released from the dust boot and joint at a location other than the intended exit point and escape path. Therefore, it is very desirable to develop greaseable dust boots which overcome the aforementioned limitations of prior art devices.